They end up with the Bowl of the Winds, but they found a completely seperate ter'angreal in the Tower--or at least were on their way to finding one when they excluded Tar Valon from their search--it needn't have anything to do with the weather, either. In fact its unlikely.

 

I reckon that was one of the nine rods of dominion, the tower's 'Oath Rod.'

 

The Nine Rods of Dominion weren't ter'angreal, they were regional governers in the Age of Legends. The Oath Rod is what was called a binder, and completely seperate.

I see, I've learned something there. I still think the Oath Rod would have been it, the name 'binder' sort of makes it fit even more nicely.

They end up with the Bowl of the Winds, but they found a completely seperate ter'angreal in the Tower--or at least were on their way to finding one when they excluded Tar Valon from their search--it needn't have anything to do with the weather, either. In fact its unlikely.

 

I reckon that was one of the nine rods of dominion, the tower's 'Oath Rod.'

It would appear it involves more than just channeling. The Light was able to stop a plot to do precisely what you suggest, and it was this which began the war of the shadow, so yeah... it likely involves some effort, or specific machinery that can be easily neutralized. I've speculated in the past that maybe the ter'angreal Nynaeve and Elayne found in the Tower using need in TAR that could help Rand, and bind the Aes Sedai to him, was involved in the drilling of the bore (and thus could be used to help the sealing). If it required a lot of people and effort it would explain both why it would bind the Aes Sedai to him--because both he and they would be needed--and why the Light was able to thwart the Shadow's use of it.

 

Whao! What!?! I think I've overlooked something huge in the series. What ter'angreal is this?

Bowl of the winds. The thing that they stop the heatwave with and give to the Sea Folk.